Disposable packaging is widely used for a variety of products, including both hot and cold convenience foodstuffs and beverages such as hamburgers, french fries, coffee, sandwiches and the like. Disposable packaging is convenient because it is inexpensive, requires no washing and can be discarded after use.
Commercially available disposable packaging suffers from a number of disadvantages, one of the most significant being environmental problems. Such packaging is typically made from oil-based plastics or other artificial materials such as polystyrene foam. These materials are not biodegradable and are disposed of in landfill sites where they accumulate and persist indefinitely as environmental contaminants. Packaging derived from paper products is manufactured using a process that requires the destruction of forest reserves and produces contaminating byproducts. Currently available disposable packaging is also expensive to produce.
Biodegradable containers have been reported for use in packaging foodstuffs. U.S. Pat. No. 3,549,619 to Mark and Mehltretter teaches a method for the preparation of amylose acetate dispersions capable of yielding edible transparent films suitable for packaging of food. The water-soluble food packaging films are produced from high amylose corn starch acetylated with acetic anhydride. The resulting corn starch acetate granules are cooked by steam jets at 177.degree. C. to disintegrate the granules. Water-soluble food packaging films are then cast from the resulting amylose acetate aqueous dispersions. The product is a water-soluble, edible, flexible film which is especially suited to package dry foods intended to be added to liquid prior to use, such as coffee or soup.
Biodegradable polymers, such as starch, have been incorporated into oil-based plastics. A corn starch-based additive is often used at a concentration of between 6 and 15% of the final product. In the appropriate environment, such as a landfill site, microorganisms digest the starch. Bulk biodegradation occurs at concentrates approaching 50% starch but, as the percentage of starch increases there is a concomitant loss of physical properties of the plastic (See Modern Plastics Encyclopedia Mid-October 1990 issue p. 178).
United Kingdom patent application No. 2,029,836, discloses a method and composition of materials for preforming starch with a lubricating fluid into pellets for use in the extrusion of biodegradable plastic. However, so called biodegradable plastics are comprised of traditional oil-based plastic polymers loaded with starch or other rapidly decomposing material as a binder. The binding material breaks down rapidly but leaves small particles of the plastic polymer which are not biodegradable. The oil-based plastics blended with biodegradable materials such as starch have not gained commercial acceptance because they are not fully biodegradable and they are expensive to produce.
Natural polymers which can be processed by conventional plastics technology have been obtained as fermentation products from single cell microorganisms. Biocycle, March 1989, p. 58 discloses the isolation of a biodegradable polymer poly(3-hydroxybutyrate-3 hydroxyvalerate). However, the polymer is expensive to produce and can not compete commercially with oil-based plastics.
Biodegradable containers which disintegrate when placed in the ground are known for use in plant cultivation and transplantation. These biodegradable plant transplanter containers may be manufactured from polymers such as polylactones or oxyalkanoyl polymers and naturally occurring biodegradable material such as rice hulls, brewers yeast, fir bark or cellulosic products. European Patent Application No. 355,250 discloses a porous container for plant cultivation prepared by mixing rice grain husks with water and a polyurethane prepolymer, moulding to the desired shape and air drying.
There is a need for biodegradable packaging material derived from natural products which is environmentally friendly and prepared by a commercially useful process. In particular there is a need for biodegradable packaging suitable for packaging a wide variety of foodstuffs including hot and cold liquids and hot foods with a high fat content, such as hamburgers and french fries.